The gypsy moth is considered to be the most destructive forest pest in the country. When they're caterpillars, they have a voracious appetite for almost any kind of tree or bush, and they can strip a tree bare overnight.

The traps contain a sex pheromone that attracts male moths and a sticky inner coating to capture the insects.

If the traps catch enough moths, the state will spray insecticide to prevent an infestation. Last year, the traps caught only 16 moths – but that’s enough to trigger a spray, says Mike Louisell with the Department of Agriculture.

"It's not the number of moths that determine[s] whether there's a spray operation," he says. "It's, what's the total evidence we have that it could continue to grow from a small infestation to something that could get out of hand?"

Then they'll spray ...

The state will set 18,000 traps in urban, rural, and forest areas over the coming weeks. The traps are small, colorful cardboard boxes nailed to tree trunks. They’re non-toxic, and if trappers do need to spray an area, Louisell says they’ll use an EPA-approved insecticide that’s safe for humans and animals.

It's called Btk, and it's been used in the U.S. since the 1970s. Although the EPA has determined that BtK is ultimately not harmful to humans, the Department of Agriculture states on its website that some people experience mild reactions to the pesticide:

"Some people have reported mild skin reactions or mild eye, ear, and nose irritations after Btk treatments. Others have reported mild hay fever reactions. Health officials have studied these reports extensively and have not been able to determine if the reactions were caused by Btk or by pollens, molds, or dust generated during the treatments, or were unrelated to Btk treatments. Public health officials state Btk is not a public health risk."

The Department of Agriculture's website also recommends that people with weakened immune systems stay inside for 30 minutes after spraying as an extra precaution:

"Remain indoors for at least 30 minutes after a spray application, particularly those with leukemia, HIV, respiratory disorders, other immune deficiencies, those receiving radiation or chemotherapy, those with allergies, and those prone to respiratory irritation. Children should wait until moisture from the spray and dew has dried on grass and shrubs before playing outside. If you come in contact with the wet spray, wash the affected skin with soap and water."

Louisell says you’ll be notified if any traps are placed on your property. You can also call the Department of Agriculture and ask to be notified about sprayings scheduled in your area.

The state is focusing its efforts on King and Pierce counties, which tend to have more moths. If you see evidence of gypsy moths in your area, you can call the Department of Agriculture’s gypsy moth hotline at 1-(800)-443-6684.